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From: "hubicka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/103903] New: Loops handling r,g,b values are not
 vectorized to use power of 2 vectors even if they can
Date: Tue, 04 Jan 2022 15:17:52 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103903

            Bug ID: 103903
           Summary: Loops handling r,g,b values are not vectorized to use
                    power of 2 vectors even if they can
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hubicka at gcc dot gnu.org
  Target Milestone: ---

This is another textcase comming from Firefox's LightPixel. I am not sure if
this is duplicate, but I think it is quite common in programs dealing with =
RGB
values.

To match the vectorized code we would need to move from SLP vectorizing the=
 3
parallel computations to vectorising the loop.

struct a {float r,g,b;};
struct a src[100000], dest[100000];

void
test ()
{
  int i;
  for (i=3D0;i<100000;i++)
  {
          dest[i].r/=3Dsrc[i].g;
          dest[i].g/=3Dsrc[i].g;
          dest[i].b/=3Dsrc[i].b;
  }
}

is vectorized to do 3 operaitons at a time, while equivalent:

float src[300000], dest[300000];

void
test ()
{
  int i;
  for (i=3D0;i<300000;i++)
  {
          dest[i]/=3Dsrc[i];
  }
}

runs faster.=